1. Technical Field of the Invention
This invention relates to substrate processing apparatus and method for cleaning a semiconductor wafer substrate in the production of semiconductor devices.
2. Description of the Related Art
In the manufacture of semiconductor devices, it is required to maintain high cleanness of both sides of each semiconductor wafer (called as “wafer” hereinafter), especially, high cleanness of a wafer's surface on which a semiconductor device is formed. In this view, it is performed to clean (wash) both sides of each wafer before and after various manufacturing processes.
In a photo-lithography process, particularly, it is indispensable to clean both sides of the wafer. In this process, for example, a scrub cleaning is performed to remove various contaminants from the wafer. In the cleaning, the wafer is accommodated in a cup for preventing scattering of cleaning liquid or collecting the cleaning liquid after use, for waste. Then, the cleaning liquid is supplied on an upper face of the wafer while rotating it in the cup. While supplying the cleaning liquid, it is further performed to make a rotating brush abut on the upper face of the wafer and further reciprocate the brush between the center of the wafer and its periphery. In this way, contaminants, such as particles, adhering to the upper face of the wafer are removed in a scrub cleaning.
In the scrub cleaning of late years, besides the cleaning using the rotating brush, it is attempted to eject an ultrasonic cleaning water or a mixture fluid (two-fluid), which is obtained by mixing inert gas with pure water, onto the wafer through a nozzle, thereby removing finer particles from the wafer.
However, the above wafer cleaning on the ejection of the cleaning liquid, such as ultrasonic water and two-fluid, causes the so-ejected cleaning water to rebound from an inner wall of the cup accommodating the wafer, in the form of a mist. Consequently, particles etc. adhering to the inner wall of the cup are sprinkled around together with the rebounding mist. Then, the so-scattered particles stick to the wafer. Essentially, the cup is intended to prevent the cleaning liquid from being scattered around during the cleaning process of the wafer and also allow the cleaning liquid to fall along the inner wall of the cup. Nevertheless, when using the cleaning water, such as ultrasonic water and two-fluid, the cleaning liquid is apt to rebound from the inner wall of the cup due to a great amount of flow rate and the intensity of ejection.
In case of a hydrophilic wafer to be processed, there is no problem because a contact angle of the cleaning liquid, which includes particles adhering to the wafer, with a wafer surface is so small that the cleaning liquid is easy to fall down from the wafer together with the particles. While, in case of a hydrophobic wafer to be processed, the contact angle is so large that wetness is deteriorated. There is a tendency for the hydrophobic wafer to expose its surface to the outside despite that the cleaning liquid is being ejected. In such a case, a problem arises in that so-called “misty particles” adhere to the wafer surface directly. It is difficult to remove the so-adhered particles from the wafer.